Acute hypoxia decreases cardiac response to catecholamines in exercising humans.

Cardiac chronotropic response to adrenergic activity at rest and exercise has been studied in 8 sea-level natives on the first two days of exposure to high altitude hypoxia (3823 m, 473 mmHg). Maximal O2 uptake (VO2max) was determined at low altitude (day 0:D0) and high altitude (day 2:D2). Submaximal exercise tests were performed at low altitude (day 1:D1) and high altitude (days 3 and 4: D3, D4). Plasma venous norepinephrine (NE) and epinephrine (E) concentrations were determined at rest and at the end of submaximal exercise. From D0 to D2, maximal heart rate decreased by 7% (p less than 0.01), and VO2max decreased by 17% (p less than 0.01). During submaximal exercise, plasma NE did not vary significantly (D1: 1.36 +/- 0.57, D3: 1.48 +/- 0.51, D4: 1.31 +/- 0.54 ng.ml-1). In contrast, relative work load decreased at high altitude (% VO2max at D1, D3 and D4 were respectively: 90.2 +/- 6.1, 83.3 +/- 9.8, 76.9 +/- 8.2). Linear relationships were found, both at low and high altitudes, between NE and VO2, NE and % VO2max, and between the increases in NE and heart rate during exercise. Covariance analysis indicates that these relations shifted to the left at high altitude:for the same NE or increase in NE, VO2 or increase in heart rate was lower at high altitude. Variations in E were similar but not significant. We conclude that hypoxia induced a decrease in cardiac chronotropic response to adrenergic activation during submaximal exercise.

[Plasma catecholamines in dogs during cold exposure and muscular exercise at the same level of energy expenditure]. / Catécholamines plasmatiques chez le chien soumis au froid et à l'exercice musculaire à dépense énergétique équivalente.

Plasma epinephrine, norepinephrine and substrate concentrations (glycemia, free fatty acids (FFA), lactic acid) have been compared in same dogs exposed to cold then made to perform a running test. Under both conditions energy expenditure was increased to the same level for each dog, approximately 7 fold the metabolic rate at rest: 1. Catecholamines were increased in cold exposed as well as in running dogs. However plasma epinephrine and norepinephrine concentrations were respectively 2,5 and 3 times higher during cold exposure than they were during muscular exercise. 2. Under both conditions hyperglycemia was observed; however it was more noticeable during cold exposure than during running. Lactic acid increased under both conditions but average concentrations were not significantly different. FFA were increased only during cold exposure. 3. It may be concluded that for the the same level of energy expenditure a greater degree of involvement of the adrenal medulla and sympathetic nervous system is to be found during cold exposure than during exercise. This difference may partly explain that the relative contribution of substrates to the energy expenditure could be different during cold exposure and muscular exercise.

Plethysmography study and pulmonary function in well-trained adolescents.

The values of lung volumes (VC, FRC, TGV, FEV1.0, etc.) and airway resistances (Raw, Raw) were measured by the spirometry and plethysmography method in 35 physically well trained, healthy adolescents, aged 14 to 20 years, boys and girls coming from various schools from the Grenoble area. The data were correlated with body height and some also with age or weight through linear, exponential or power law relationships. All volumes increased with height (Ht), which was the best independent variable, with some preference for a linear representation. However the increase of lung volumes with height was also well reproduced by an exponential function proportional for all volumes to e0.020Ht in good agreement with recent results obtained for young children. Some significant sex differences were observed for lung volumes. Airway resistance measured by two different methods (Raw and Raw) decreased with height with some preference for a linear relationship. The mean airway resistance (Raw) obtained from a complete inspiration-expiration curve while the subject breathed at his own spontaneous breathing rate was systematically smaller (from 0.5 to 1 cmH2O/l/s) than Raw measured by a technique similar to the panting method. No sex differences for airway resistances or conductances were observed. Specific airway conductance was found to be age and height independent.

Maximum oxygen consumption in dogs during muscular exercise and cold exposure.

Maximum oxygen consumption for a short exhaustive work (Ex VO2 max) and for a severe cold stress (C VO2 max) were investigated in 8 dogs. Heart rate, plasma catecholamines and substrate concentrations were measured under both conditions. Mean C VO2 max was lower than mean Ex VO2 max. Heart rate and plasma lactate were also lower during cold exposure than during exercise. Average plasma epinephrine concentrations were not significantly different and average plasma norepinephrine concentrations were similar under C VO2 max and Ex VO2 max conditions. A positive correlation was found between plasma lactate and epinephrine concentrations measured under both conditions. It may be assumed that maximum oxygen consumption during muscular exercise is higher than during shivering thermogenesis. This difference does not seem to be due to differences in the involvement of the sympathico-adreno-medullary system.

Liver heat production and temperature regulation in the anesthetized dog.

Liver heat production (LHP) was measured in the anesthetized dog by a new calorimetric method. Blood flows and temperatures were measured at the same points. The method avoided damage of liver innervation and vascularization. Changes of LHP were investigated under different thermal conditions. Measurements at controlled arterial temperatures within the physiological range showed changes of LHP when arterial temperature was randomly increased or decreased. When measured LHP was compared in experiments carried out at different ambient temperatures, a negative linear correlation was found between LHP and the ambient temperature. It was concluded that liver heat production may be a factor in temperature regulation.

Calorigenic effect of insulin in hypothermic dogs.

In dogs acutely immersed in cold water (8--13 degrees C), oxygen uptake increased approximately sevenfold and colonic temperature rapidly began to decrease. Fifteen minutes after the start of immersion a high level of hyperglycemia was found but no increase in immunoreactive plasma insulin level was observed. Under these conditions exogenous insulin (0.3 U.kg-1) induced a further increase in oxygen uptake and in shivering intensity whereas a decrease in the fall of colonic temperature was observed. It can be concluded that insulin may have a calorigenic effect and improve the resistance to cold of dogs exposed to an acute cold stress.

Catecholamines in dogs during cold adaptation by repeated immersions.

Dogs were immersed in cold water 1 h/day for 30 consecutive days. During the first immersion, oxygen uptake increased approximately sevenfold and colonic temperature decreased; a large increase in plasma epinephrine and norepinephrine concentrations was found; plasma glucose, lactic acid, and free fatty acid (FFA) concentrations were also increased. An adaptative response to cold was evidenced during the 10th immersion by a further increase in oxygen uptake and a reduction in the fall of colonic temperature; plasma epinephrine, glucose, and lactic acid were diminished whereas FFA were higher. Consequently 10 h spent in cold are sufficient to induce an improved capacity for heat production. An enhanced ability to produce nonshivering thermogenesis mediated by epinephrine or norepinephrine is not obvious because after the 30th immersion no enhanced calorigenic response to epinephrine or norepinephrine infusion was found. In dogs mechanisms other than norepinephrine-enhanced sensitivity might be involved in this kind of cold adaptation.

Plasma O-methyldopa in levodopa-induced dyskinesias. A bioclinical investigation.

The peripheral metabolism of Dopa has been studied in correlation with the clinical occurrence of Leyodopa-induced dyskinesias in Parkinson patients. Within the group of patients treated with a peripheral decarboxylase inhibitor (PDI), the combination of all the plasma levels of O-Methyldopa from patients with dyskinesias shows significantly higher values than those from patients without dyskinesias. For Dopa itself, no significant differnece can be detected. Such high O-Methyldopa levels seem to be due to a progressive accumulation of this compound and not to a higher degree of formation. In contrast, no significantly different Dopa or O-Methyldopa levels are found within the group of patients treated with L-Dopa alone. These results are discussed in relation to some of the suspected mechanisms involved in Levodopa-induced dyskinesias.

[Results of determination of plasma methoxydopa in parkinsonian patients with or without dyskinesia induced by L-Dopa]. / Résultats des dosages de la méthoxydopa plasmatique chez les parkinsoniens avec ou sans dyskinésies induites par la L-DOPA.

Horary plasmatic dosages of Dopa and metabolites in 30 treated parkinsonian patients have shown that, within the group of patients treated with L-Dopa combined with an extracerebral decarboxylase inhibitor, highly significant by increased plasmatic O-methyl-dopa levels can be found in patients with dyskinesias compared with those without dyskinesias. On the contrary, in these two subgroups of patients, plasmatic Dopa levels are not significantly different. By comparing some favoured Dopa and O-methyl-dopa levels between these two subgroups of patients, it seems more likely, that the elevated plasmatic O-methyl-dopa levels are due to an progressive accumulation on of its compound than to an excessive formation from Dopa.

Does O-methyl-dopa play a role in levodopa-induced dyskinesias?

Clinically scored levodopa-induced dyskinesias were correlated with plasma dopa and O-methyl-dopa levels determined every hour during one day in 30 Parkinsonian-treated patients. In patients treated with a combination of L-dopa and a peripheral decarboxylase inhibitor (PDI), those with dyskinesias have very high plasma O-methyl-dopa levels compared with those who have no dyskinesias. In contrast, no significantly different plasma dopa levels are found in these two subgroups of patients, leaving open the question of the possible involvement of such elevated plasma O-methyl-dopa levels in favouring dyskinesias.

[Recording of the cardiac magnetic field. Technical considerations and initial results in hospital practice]. / L'enregistrement du champ magnétique cardiaque. Considérations techniques et premiers résultats en milieu hospitalier

Recording the magnetic field of the heart poses enormous technical problems. Whatever type of captor is used, the parasite magnetic fields are 11000x more powerful than those of cardiac origin, and must be excluded. It is for this reason that magnetocardiography has remained a laboratory technique until the last few years. The authors present an induction magnetocardiograph whose specifications make it suitable for use in hospital practice. Thanks to the selectivity of the captor, it is possible to produce magnetic plots of the thorax.

[Action of thyroid hormones on the calorigenic effect of adrenaline]. / Influence des hormones thyroïdiennes sur l'effet calorigénique de l'adrénaline

The present investigation was undertaken in order to appraise the interaction between thyroxine and epinephrine in dogs exposed to acute cold. In normal, then successively thyroidectomized, adrenal demedullated and thyroxine restored dogs, epinephrine was infused in basal condition and during acute cold exposure. In thyroidectomized dogs epinephrine lost its calorigenic effects. So it did in thyroidectomized and adrenal demedullated dogs. Conversely, when dogs were restored in thyroxine, epinephrine recovered its calorigenic effect. Evidence for thyroxine-catecholamine interaction can be seen in basal condition as during acute cold. Nevertheless, this interaction is more obvious during shivering thermogenesis.